2.0 Analysis 2.1 General The Cessna pilot's decision making and airmanship, as well as the controller's use of ad-hoc procedures were significant factors contributing to this occurrence. The analysis will concentrate on the interactions between the Cessna206 aircraft pilot, the airport controller, and the NWA971 flight crew. 2.2 Cessna 206 Pilot's Actions While being sequenced for arrival at Toronto/LBPIA, and within three miles of the runway, the Cessna206 pilot accepted a LAHSO clearance for a landing on Runway05. Although, in theory, a pilot in this situation should have referred to the airport diagram and determined whether this was an approved procedure, it is not unreasonable to expect a pilot to assume it is approved. Firstly, the pilot had little time to review the aerodrome chart, and the aircraft was close to landing. Secondly, the controller initiated the LAHSO request, and the pilot would, in all likelihood, assume that the request to land and hold short was a legitimate clearance. When the pilot of the Cessna206 observed that the right main landing gear green light did not illuminate, it would have been prudent for him to communicate the information to the controller, including the possibility that a go-around would be required. The difficulties with the landing gear system certainly presented the possibility that the pilot would have to go around or that the aircraft could not land on Runway 05 and stop before the intersection of Runway33L. 2.3 Airport Controller's Actions Sequencing of arriving and departing traffic using intersecting runways requires precise timing and an appreciation of aircraft performance capability on the part of the controller. To maximize the flow rates for departures and arrivals, clearances must be issued so the spacing between aircraft is optimized. The controller had to contend with a high departure demand from Runway33L and a low arrival rate on the crossing runway, Runway05. Only sequential operations are available to the controller when using 33L/05runway pairing. There are differences in the two types of procedures, which essentially depend on when an arriving aircraft crosses the landing threshold and when a departing aircraft crosses the intersection of the two runways. In either sequential or simultaneous operations, both aircraft may be in receipt of a landing or a take-off clearance. For sequential operations, the controller must ensure that the landing aircraft does not cross the threshold of the landing runway until the departing aircraft has crossed the intersection of the two runways, or the departing aircraft does not commence the take-off roll until the landing aircraft has safely landed and has slowed to taxi speed or has stopped prior to the intersection. Although not specifically required, the controller may pass traffic information to the restricted aircraft, that is, the aircraft required to hold short of the intersection. The controller was using this type of operation between the Cessna206 and the American Airlines Boeing737 (AAL449) that departed just prior to NWA971. AAL449 departed Runway33L and crossed the intersection of Runway05 well before the Cessna206 crossed the threshold of Runway05. Traffic information was passed to both AAL449 and the Cessna206. The Cessna206 is a relatively slow aircraft and was 2.5miles from the threshold when AAL449 departed. The controller then authorized the next aircraft in sequence, NWA971, to taxi to the take-off position on the runway. Continuing with sequential operations, he would have had to wait until the Cessna206 had landed and slowed to taxi speed before issuing a take-off clearance to NWA971; the wait would have been approximately 45-50seconds. This would have assured the required spacing between the two aircraft. With a line of approximately 15-20aircraft waiting for departure, the controller made a conscious decision to transition from a sequential to a simultaneous operation. The controller was, from previous controlling experiences with small aircraft, aware of the performance capability of the Cessna206, and that the available runway from the threshold of Runway05 to the intersection with Runway33L was adequate for the aircraft to land. He did not accurately assess the possibility of a go-around when planning the use of simultaneous procedures. With the Cessna206 already cleared to land, with the restriction to hold short of Runway33L, the controller issued traffic information and a departure clearance to NWA971. NWA971 read back the clearance and continued with a rolling take-off, while the Cessna206 was just crossing the threshold of Runway05. The controller did not advise the pilot of the Cessna206 that an aircraft was departing from an intersecting runway, as required by ATC MANOPS352.6(I). The controller was now using LAHSO reserved for simultaneous operations, which were not authorized for this runway pair. The controller was not aware that the pilot of the Cessna206 was experiencing landing gear problems and, thinking the aircraft had landed and was on the roll out, issued taxi instructions to the Cessna pilot and repeated the instruction to hold short of Runway33L. With approximately 3350feet of runway remaining prior to the intersection of Runway33L, the Cessna pilot commenced a go-around, and so informed the controller. The two aircraft were now both heading for the intersection of the two runways. The controller immediately told the Cessna pilot to turn left. However, he did not advise the pilot of the conflicting traffic, nor did he instruct the Cessna pilot to remain clear of Runway33L. The risk of the Cessna206 aircraft encountering the wake vortex of either the previously departed Boeing737 or the McDonnell Douglas DC-9 aircraft was not considered by the controller. The controller, as a result of the long line of aircraft awaiting departure, used an unauthorized procedure in an effort to maintain a high traffic flow rate. This increased the risk of collision in the event of a go-around by the arriving aircraft because of the proximity of the runway intersection to the runway threshold. The controller's decision was reinforced by his previous operational experience controlling small aircraft such as the Cessna206, which led him to believe that the Cessna pilot would have no trouble complying with the hold short clearance. 2.4 NWA971 Flight Crew Actions As the crew of NWA971 waited in line for take-off sequencing, they heard the communication between the controller and AAL449 referencing the Cessna206 which was cleared to land on Runway05 and hold short of Runway 33L. After AAL449 departed, the controller then passed traffic information on to the NWA971 flight crew, advising them that the Cessna206 was about to touch down and that it would hold short of Runway33L. The controller then cleared NWA971 to take off from Runway33L, and the flight crew accepted a LAHSO clearance. Again, as for the Cessna pilot, the crew would, in all likelihood, accept the clearance as legitimate. The crew did not recall hearing the report by the pilot of the Cessna206 that he was commencing a go-around; both aircraft were on the same frequency. Upon recognition of the impending conflict, the flight crew took appropriate evasive action and then proceeded to their destination. The pilots of participating aircraft may not be aware of the type of operation, sequential or simultaneous, the controller is conducting. The aerodrome chart used by the Northwest Airlines crew depicted LDA for runway pairs specifically authorized for LAHSO; however, there was no specific identification of LAHSO terminology in the chart depiction. Reference to LAHSO terminology may have increased the flight crew's awareness of authorized operations. Further, the LAHSO procedure employed by the controller was not included on the ATIS or other ATC advisories. This omission was not sufficient to alert the pilots that LAHSO was not an authorized procedure for this runway pairing and that the procedure should not have been accepted. 3.0 Conclusions 3.1FindingsastoCausesandContributingFactors Because of the backlog of departing traffic and in an effort to expedite departures, the controller chose to use land and hold short operations (LAHSO) instead of sequential runway operations, which ultimately resulted in a near collision. The controller used LAHSO procedures between a departing and arriving aircraft on a runway pair for which this procedure was not authorized. The Cessna pilot had a landing gear problem; however, he did not advise the controller of the problem or of the risk that he may not be able to land on Runway05 and stop before the intersection of Runway33L. The controller did not advise the Cessna pilot that a DC-9 aircraft was departing from Runway 33L at the same time the Cessna 206 was landing on Runway05. The controller did not advise the Cessna pilot of conflicting traffic when he issued evasive instructions, and he did not instruct the Cessna pilot to remain clear of Runway33L. The controller did not accurately assess the possibility of a go-around when planning the use of simultaneous procedures. 3.2 Findings as to Risk The aerodrome chart used by the Northwest Airlines flight crew did not specifically identify LAHSO terminology in the depiction of LAHSO data for Toronto/Lester B. Pearson International Airport, and, as a result, the flight crew may not have been aware of which LAHSO operations were authorized. There are no published air traffic control (ATC) procedures for aircraft to follow in the event a go-around is necessary by a landing aircraft after the pilot has accepted a hold short clearance and is unable to comply with the restriction. The risk of an encounter by the Cessna206 aircraft with the wake vortex of either the previously departed Boeing737 aircraft or the DC-9 aircraft was not considered by the controller or the Cessna pilot. 3.3 Other Findings The LAHSO procedure used by the controller was not included on the automatic terminal information service (ATIS). This omission was not sufficient to alert the pilots of either aircraft that LAHSO was not an authorized procedure for this runway pair. Because of restrictions imposed for noise mitigation purposes, runways33R and33L are not available for routine departure and arrival operations, which exacerbates the complexity of air traffic control operations. 4.0 Safety Action 4.1 Action Taken 4.1.1 Eagle Aircraft Inc. Eagle Aircraft Inc., based at Toronto/City Centre airport, conducted a maintenance inspection on the Cessna206, C-GGSG, upon its arrival at Toronto Island. The aircraft maintenance engineer submitted to Transport Canada a service difficulty report (SDR), control numberCF20020906001, which related information about the failure of the right main gear actuator link. 4.1.2 Transport Canada As a result of this occurrence, Transport Canada, in September2002, conducted an on-site regulatory audit of the Toronto/LBPIA air traffic control tower, The objective of this audit was to examine the unit's compliance with the Canadian Aviation Regulations (CARs) and associated standards, including a review of the corrective action plans following the previous audit and inspection. The audit findings revealed a non-conformance to the CARs and the associated Canadian Domestic Air Traffic Control Separation Standards in that a tower controller authorized an aircraft to depart a runway while an arriving aircraft was landing on an intersecting runway resulting in a loss of separation where both aircraft converged in close proximity to each other. A detection Notice was filed with Transport Canada Ontario Region Enforcement Branch for further action. The audit findings also identified two observations dealing with administrative elements not pertaining to this occurrence. 4.1.3 Transportation Safety Board of Canada On 19 November 2002, the Transportation Safety Board of Canada issued an Occurrence Bulletin to Transport Canada noting that land and hold short operations (LAHSO) awareness is not maximized in the presentation of LAHSO data on all Canada Air Pilot charts and some Jeppesen charts, in that there is no specific identification of LAHSO terminology on any of the applicable charts. 4.1.4 Jeppesen Sanderson The applicable Jeppesen charts, Canada Air Pilot charts, and A.I.P. Canada Section RAC 4.4.9 Operations on Intersecting Runways were reviewed by the Jeppesen Chart Display Standards group. It was decided that the column title for available landing distances for simultaneous runway operations depicted on the Jeppesen Airport Additional Runway Information band be titled LAHSO Distance instead of Threshold to Intersecting Runway. Revision of affected charts began on 03October2003.